Tumor cells appear to have a greater avidity for amino acids than normal cells, as judged by the fact that under conditions of starvation amino acids are transferred from normal to neoplastic tissues. The proposed research represents an approach to understanding the basis of this phenomenon. In addition, we wish to determine whether there is anything specific about the process of amino acid transport in neoplasms which might provide a basis for the specific limitation of tumor growth through nutrient deprivation. The problem will be approached by using mouse mammary glands in several normal, preneoplastic and neoplastic states including virgin, pregnant, lactating, involuting tissues as well as hyperplastic alveolar nodule outgrowths, adenocarcinomas and ascitic tumors. In studying tissues in these various states, we will examine the types of transport system present, their capacity, and their specificity, in order to determine by what mechanisms amino acid transport is altered to meet the requirements of protein synthesis. We will determine whether there is a difference between transport in rapidly proliferating tissue (pregnant, neoplastic) and that seen in a well-differentiated state in which amino acids are rapidly accumulated (lactation). The role of insulin in pregnant tissue will be examined. We will determine whether the characteristics of transport in a cultured mammary tumor cell line are similar to those of freshly isolated normal or tumorous tissue. In addition to providing important information about amino acid transport in malignant tissues, these studies are designed to develop better understanding of the mechanisms by which amino acid transport is regulated to meet the substrate demands of tissues which are actively synthesizing protein for growth or secretion.